There is also precedent for the court to block impeachment: in 2004, then-President Roh Moo-hyun was removed by parliament for alleged election law violations and incompetence.
But the Constitutional Court later reinstated him.
The court also currently only has six judges, meaning their decision would need to be unanimous.
And should the vote fail, Yoon can still face "legal responsibility" for the martial law bid, Kim Hyun-jung, a researcher at the Korea University Institute of Law, told AFP.
"This is clearly an act of insurrection," she said.
"Even if the impeachment motion does not pass, the President's legal responsibilities under the Criminal Code... cannot be avoided."
'So angry'
Yoon has remained unapologetic and defiant as the fallout from his disastrous martial law has deepened.
In a televised address, he vowed on Thursday to fight "until the very last minute" and doubled down on unsubstantiated claims the opposition was in league with the country's communist foes.
Thousands have taken to the streets of Seoul since Yoon's martial law declaration to demand his resignation and jailing.
Yoon's approval rating -- never very high -- has plummeted to 11 percent, according to a Gallup Korea poll released Friday.
The same poll showed 75 percent now support his impeachment.
Protesters run the gamut of South Korean society -- from K-pop fans waving glowsticks to retirees and blue-collar workers.
"Impeachment is a must and we must fight relentlessly," Kim Sung-tae, a 52-year-old worker at a company that makes car parts, told AFP.
"We're fighting for the restoration of democracy."
Teacher Kim Hwan-ii agreed.
"I'm so angry that we all have to pay the price for electing this president."